Hi Cls67,
Thanks for reaching out to the community! I understand you'd like to use a Chromecast device on your TV. Specifically, you're looking to connect your Android phone to cast content already downloaded on YouTube, either through your Roku streaming stick or your TV's YouTube app. I'll be glad to provide the information you need!
Chromecast device and Roku are kind of like two different brands of video players, each with its own way of working. You can't really plug one whole video player into another one to make it work.
The Roku stick just plugs into your TV's HDMI port to become the smart part of your TV, letting you stream apps. It doesn't have a spare port to plug a Chromecast device into, and they're designed by different companies to do the same sort of thing in their own way.
If you have any other questions, please don't hesitate to post them on this forum.
Best regards,
Juan
